Thousands of websites, including some of the most popular, are going dark today to protest the Stop Online Piracy Act, which is designed to thwart copyright infringement but that Web experts warn could threaten the functionality of the Internet.

Encyclopedia giant Wikipedia, popular news-sharing site reddit, browser pioneer Mozilla, photo-sharing favorite Twitpic and even ICanHazCheezburger.com are blocking access to content throughout Wednesday, symbolizing what the bill may allow content creators to do to sites they accuse of copyright infringement. Other websites, including Google, are expressing solidarity with the protests by featuring anti-SOPA content on home pages.